Lawn mowers, particularly self-propelled machines fitted with rotating blades for cutting grass and other vegetation, can produce uneven cuts and transmit unwanted stresses from the terrain to the driver and mower, resulting in driver fatigue and discomfort, mower wear and tear, more frequent repairs, and a shorter mower life. In many typical mowers, the cutter deck is suspended as either a ground-following deck or a floating deck. A ground-following deck typically rides on caster wheels (e.g., a set of two or four caster wheels in many cases) and follows the contours of the ground. A floating deck is often suspended beneath the frame between the front and rear wheels, such as by chains, sets of links and other elements. Other floating decks are suspended in various manners over the ground at a location in front of, behind, or beside the lawn mower frame. The floating deck is raised when skids, wheels, rollers, or other elements attached to the deck contact the lawn surface. The height of a floating deck from the surface being cut is often defined at least in part by the elevation of the mower's frame.
Generally, the intent for such a deck suspension system is to avoid continuing contact with the earth surface. When a cutter deck travels over uneven terrain having a strong grade, the cutter deck can contact the earth surface, and can cause the lawnmower blade(s) therein to scalp the surface being cut. Cutter decks are generally designed to avoid scalping by rising or floating upwardly. This generally works for certain kinds of earth unevenness, but some scalping still occurs on severe terrain. Even if scalping can be avoided, cutter deck height relative to the earth surface can vary widely. This is also undesirable because it results in an unequal height of the cut grass.
A significant number of lawnmowers have wheels that are rigidly attached to the mower frame. Unfortunately, when a mower having such a suspension encounters uneven terrain, the mower frame can respond with significant upward and downward movement. With regard to lawnmower front wheels, many conventional lawn mower designs either rigidly connect the front wheels to the frame as just mentioned or employ a single axle to which the front wheels are attached. In some cases, the single axle can pivot about a point between the wheels, thereby generating slightly improved performance. Whether rigidly secured to the frame or connected to a common axle, such front suspension designs either do not eliminate the undesirable upward and downward frame movement described above, or only do so to a very limited extent. For example, if one wheel of such a mower rises in response to a rise in terrain, the single axle would cease to be parallel with the earth surface, generating forces that bring the frame and cutter deck also out of a parallel relationship with the earth surface. The resulting cut of the grass is uneven and unsatisfactory.
In these and other conventional mowers, improved spring suspension systems are employed to reduce the amount of vertical frame motion when one or more wheels encounter unevenness in the earth surface being traversed. These spring systems improve traction of such mowers by maintaining improved contact between the wheels and the surface being traversed. However, these spring suspension systems can cause or allow the frame to roll relative to the cutting surface, such as, for example, when a mower is turned sharply or navigates a steep hillside. When a frame rolls, a floating cutter deck (and in many cases, even a ground-following cutter deck) rolls with the frame, resulting in one side of the cutter deck being closer to the cutting surface than the other. Consequentially, the cut of the grass is uneven and unsatisfactory.
In some conventional mowers, caster wheels are suspended on linkages which change the camber of the wheels throughout the travel of the linkages. Such suspension designs typically allow the caster wheels to wobble like the wheels on a shopping cart, decreasing mower stability and increasing the likelihood of turf damage.
In order to address cutting quality, rider comfort, and suspension wear problems, many conventional lawn mowers employ suspensions having one or more springs. Although such spring suspensions do represent an improvement and can help to address these problems, significant room for improvement still exists. For example, heavy riders or heavy mower accessories (e.g., grass catchers) tend to exert extra stress on the suspension springs, potentially causing the suspension springs to “bottom out” or to provide a limited range of spring motion. In either case, an uncomfortable ride results because the spring has limited or no capacity to absorb shock. As a result, an increased amount of shock is transferred to the mower and operator. The increase in shock can significantly shorten the life of the mower and can be a cause of more frequent mower maintenance and repair. Substituting a stiffer spring for heavy loading situations is an unattractive solution for many reasons, such as an uncomfortable ride in a light loading situation and additional low-level vibrations transmitted to the frame.
In light of the shortcomings and problems of conventional lawn mowers described above, a need exists for a lawn mower having a suspension system that improves ride quality in a light loading situation, provides improved steering control and traction, while maintaining improved contact between the wheels and the surface being traversed, as well as improved floating cutter deck and/or ground-following cutter deck motion.